1. Field of the Disclosure
The present invention relates generally to control circuits and, more specifically, the present invention relates to control circuits used in a power converter that regulate the power converter output.
2. Background
Power converter control circuits may be used for a multitude of purposes and applications. Due to requirements to reduce power converter cost, there is a demand for control circuit functionality to reduce external component count for components external to the integrated control circuit. This reduction in external component count enables miniaturization of the power converter to improve portability, reduces the number of design cycles required to finalize a power converter design and also improves reliability of the end product. Furthermore, reduced component count can offer energy efficiency improvements in the operation of the power converter and can reduce the power converter cost. One aspect of the power converter offering the potential for component count reduction is in simplifying or removing the external circuitry previously required to achieve output voltage regulation in a power converter.
In isolated flyback converters used for AC/DC power conversion, the output voltage is typically measured across the isolated power supply output terminals to generate a continuous feedback signal that is coupled to a control circuit on the primary, also referred to as the input, of the power supply, typically employing an opto-coupler to provide isolation between power supply input and output circuitry. The control circuit is responsive to the feedback signal to control switching of a power switch coupled to a winding of an energy transfer element to regulate power delivered from the input to the output of the power converter.
In other flyback converters, a feedback signal is generated using an auxiliary winding forming part of the power converter transformer or energy transfer element. The flyback voltage across the auxiliary winding is rectified and smoothed to generate a feedback signal that is coupled to a control circuit on the primary side of the converter.
In buck converters a feedback signal representative of the power converter output voltage is typically generated by rectifying and smoothing the voltage across the main inductor or energy transfer element winding during the off time of a power switch.
In both flyback and buck converter configurations, the power switch is coupled to a power supply input and to the energy transfer element such that a current flows from the power supply input through the power switch and the energy transfer element when the power switch is in an ON state.